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The Quadrilátero Ferrífero (QF) is a globally known region for its world-class metallic deposits. Although its Precambrian units have been vastly studied since the 1960s due to economic importance, the Cenozoic geological record represents an upcoming subject of interest. The occurrence of Cenozoic sedimentary deposits has been noticed since the end of the 19th century, but most of them are not yet fully characterized. This paper brings a complete description, mapping, 3D modeling, and simulations of the sedimentary deposit named Bandeira Basin, Serra do Tamanduá, QF. Based on field data, such as mapping and drill core database analysis, three drill cores were selected for further investigation and detailed description. The Bandeira Basin can be characterized and subdivided into three units: Unit A: found only in the southeast area and shows exclusively sediments from the Nova Lima Group; Unit B: intermediate unit that occurs in central and southeast areas, with Rio das Velhas Supergroup as a possible source of the sedimentary material; and Unit C: occurs at the top, and it is essentially colluvial deposits from Minas Supergroup units. The contacts between units are abrupt or erosive, recording successive deposition stages. The basin is thicker on its central and southwest ends and thinner on the east and north, where part of the basement outcrops. Cenozoic tectonic events were probably active in this area, controlling the sedimentary processes, with the NW-SE and NE-SW lineaments reactivated, triggering sediment deposition and migration to the deepest spot of the basin. These sediments were 3D modeled in Leapfrog Geo, the visualization of any given region of interest, in the modeled scale. This methodology allowed an assertive characterization of sedimentary filling and could be applied to other basins. This comprehension is important because these sediments are used indirectly or directly in civil projects. [ABSTRACT FROM AUTHOR]

A synthesis of the evolution of the Neoproterozoic belts or orogens surrounding the São Francisco craton (SFC) in northeastern and southeastern Brazil is presented. Emphasis is placed on recognizing the superposition of sedimentary basins, from rift to passive margin to retroarc and foreland, as well as identifying three diachronic continental collisions in the formation of the SFC. The Tonian passive margin occurs in the southern Brasília Belt with the Vazante, Canastra, and Araxá Groups. During the Tonian, island magmatic arcs and basins developed in front and behind these arcs (fore- and back-arcs). Subsequently, in the Cryogenian–Ediacaran, a retroarc foreland basin developed with part of the Araxá Group and the Ibiá Group, and finally, a foreland basin developed, which was filled by the Bambuí Group. A tectonic structure of superimposed nappes, with subhorizontal S1–2 foliation, formed between 650 and 610 Ma, is striking. In the northern Brasília Belt, there is the Stenian passive margin of the Paranoá Group, the Tonian intrusion of the Mafic–Ultramafic Complexes, and the Mara Rosa Island magmatic arc, active since the Tonian, with limited volcanic–sedimentary basins associated with the arc. A thrust–fold belt structure is prominent, with S1 foliation and late transcurrent, transpressive tectonics characterized by the Transbrasiliano (TB) lineament. The Cryogenian–Ediacaran collision between the Paranapanema and São Francisco cratons is the first collisional orogenic event to the west. In the Rio Preto belt, on the northwestern margin of the São Francisco craton, the Cryogenian–Ediacaran Canabravinha rift basin is prominent, with gravitational sediments that represent the intracontinental termination of the passive margin that occurs further northeast. The rift basin was intensely deformed at the Ediacaran–Cambrian boundary, as was the Bambuí Group. On the northern and northeastern margins of the São Francisco craton, the Riacho do Pontal and Sergipano orogens stand out, showing a comparable evolution with Tonian and Cryogenian rifts (Brejo Seco, Miaba, and Canindé); Cryogenian–Ediacaran passive margin, where the Monte Orebe ophiolite is located; and Cordilleran magmatic arcs, which developed between 620 and 610 Ma. In the Sergipano fold belt, with a better-preserved outer domain, gravitational sedimentation occurs with glacial influence. A continental collision between the SFC and the PEAL (Pernambuco-Alagoas Massif) occurred between 610 and 540 Ma, with intense deformation of nappes and thrusts, with vergence to the south and accommodation by dextral transcurrent shear zones, such as the Pernambuco Lineament (PE). The Araçuaí belt or orogen was formed at the southeastern limit of the SFC by a Tonian intracontinental rift, later superimposed by a Cryogenian–Ediacaran rift–passive margin of the Macaúbas Group, with gravitational sedimentation and glacial influence, and distally by oceanic crust. It is overlain by a retroarc basin with syn-orogenic sedimentation of the Salinas Formation, partly derived from the Rio Doce cordilleran magmatic arc and associated basins, such as the Rio Doce and Nova Venécia Groups. A third continental collision event (SF and Congo cratons), at the end of the Ediacaran (580–530 Ma), developed a thrust–fold belt that deforms the sediments of the Araçuaí Belt and penetrates the Paramirim Corridor, transitioning to the south to a dextral strike-slip shear zone that characterizes the Ribeira Belt. [ABSTRACT FROM AUTHOR]

In east‐central Brazil, the Ediacaran‐Cambrian Bambuí Basin has the potential to provide a record of unique geochemical responses of Earth's ocean and atmosphere evolution during this key time interval. From this perspective, we studied an interval of the upper Bambuí Basin using sedimentologic, stratigraphic, and chemostratigraphic tools. The lower Cambrian Jaíba Member of the uppermost Serra da Saudade Formation is an interval of up to 60 m‐thick of carbonate rocks disposed into two shallowing upward trends. Inner to outer ramp and high‐energy shoal deposits are described, in which laminated microbialites are the prevailing sedimentary facies. REE + Y data suggest contamination by iron (oxy)hydroxides that are dissociated from the riverine detritic flux. Sedimentary iron enrichment may be related to the settling of iron nanoparticles in coastal environments, diagenetic iron mobilization, or both. MREE enrichment is caused by microbial degradation of organic matter in the iron reduction zone during the anoxic early‐diagenetic stage. Chromium isotopes yielded negatively fractionated values (δ53Cr = −0.69 to −0.27‰), probably resulting from biotic and abiotic reduction of dissolved Cr(VI) to light and less toxic Cr(III) within pores of microbial mats. The δ53Cr data of the Jaíba microbialite are thus a product of metabolic reactions in microbial mats and do not reflect seawater signal. The isotopic offset from seawater is feasible from molecular diffusion of Cr into pore water and reduction reactions occurring deep inside the mat, although the exact mechanism and consequences are not yet fully understood due to the poor preservation of metabolic reactions in the geological record. Our study suggests that Cr isotopes can be used to reconstruct Cr and other metals cycling within ancient microbial mats, and that caution should be taken when using past microbialites to infer seawater Cr records and redox state of the atmosphere and ocean. [ABSTRACT FROM AUTHOR]

Abstract Significant Ediacaran paleoenvironmental changes recorded in the mixed carbonate-siliciclastic Bambuí Basin, east-central Brazil, outcrop in one of the best-preserved sites, the Januária paleo-high. From a detailed stratigraphic and chemostratigraphic approach (carbon and oxygen isotopes, total organic carbon, total sulfur and selected elements abundances), we identified transgressive-regressive intervals and depositional settings within the Bambuí Group stratigraphy and developed a new model for the origin of the extremely positive Middle Bambuí Excursion (MIBE) present in the middle section of the basin. A post-Marinoan cap carbonate interval is recorded in the first ~10 m, preserving aragonite pseudomorph fans, barite-rich layers and negative δ13C anomaly. A hiatus separates the cap carbonate from the late Ediacaran succession that makes up the remaining Bambuí Group. The younger intervals preserve both siliciclastic (middle Serra de Santa Helena Formation) and carbonate (middle/upper Sete Lagoas and Lagoa do Jacaré formations) shallow-water depositional settings, requiring tectonic influence or climatic changes in source areas. The MIBE yields δ13C values as high as +14‰ and extends for about 350 m, from the upper Sete Lagoas Formation to the lower Serra da Saudade Formation. We suggest a model of a restricted basin setting that favored local carbon isotopic signals in the δ13C record of sedimentary carbonates through preferential weathering of ancient carbonate platforms on the continent and higher burial rate of authigenic carbonate. This scenario caused the global δ13C budget to be affected by an offset of, at least, +4‰ in sedimentary carbonates deposited on the São Francisco craton and along its margin during the terminal Ediacaran. Many previous studies suggested a restricted nature for the middle Bambuí Basin, which probably resulted from the central position of the São Francisco paleocontinent within the mosaic of collisional blocks during the SW Gondwana amalgamation. Highlights • A complete stratigraphic and chemostratigraphic data of the Ediacaran Bambuí Basin of Brazil. • Peritidal carbonates and sandstones to deep-water shales make up the mixed carbonate-siliciclastic sedimentation. • The MIddle Bambuí Excursion (MIBE) yields extremely heavy δ13C values as high as +14‰. • Paleogeography in the terminal Ediacaran probably had an important role in basin restriction and positive isotope excursion. [ABSTRACT FROM AUTHOR]

Stratigraphic, isotopic, and geochronological data from two late Neoproterozoic-aged conglomerate wedges in the southwest São Francisco craton support the interpretation that the Ediacaran Bambuí Group in east-central Brazil was deposited in a foreland basin. The Samburá Formation forms the base of the Bambuí Group in the southwestern part of the Bambuí basin and was deposited synchronously with the Brasília orogeny. It is interpreted to be a sedimentary product of a retrogradational coastal alluvial fan system deposited in an underfilled flexural foredeep during the early stages of foreland basin development sometime between 630 and 560 Ma. The basal Sete Lagoas Formation carbonates were deposited towards the cratonic margin on the forebulge, which provided an ideal environment for carbonate production. The lateral relationship between the Samburá and Sete Lagoas formations further implies that an unconformity was generated by foreland flexure, and that this unconformity separates an early Ediacaran phase of the foreland basin from a late Ediacaran phase. The Lagoa Formosa Formation was deposited in the latter phase, after peak orogenesis, with a provenance that includes post-orogenic granites and zircons as young as 560 Ma. It records a prograding turbidite fan system in the Lagoa Formosa Formation that was deposited during orogenic unroofing and basin-wide shallowing in a filled stage of the foreland basin. A shift from highly enriched δ 13 C values towards global-like carbon isotopes values in carbonates within the Lagoa Formation, in conjunction with the occurrence of banded iron formation, may suggest deposition in a basin with anoxic and ferruginous deep waters in the Bambuí basin in the latest Ediacaran. [ABSTRACT FROM AUTHOR]

The Carrancas Formation outcrops in east-central Brazil on the southern margin of the São Francisco craton where it comprises the base of the late Neoproterozoic Bambuí Group. It is overlain by the basal Ediacaran cap carbonate Sete Lagoas Formation and was for a long time considered to be glacially influenced and correlative with the glaciogenic Jequitaí Formation. New stratigraphic, isotopic and geochronologic data imply that the Carrancas Formation was instead formed by the shedding of debris from basement highs uplifted during an episode of minor continental rifting. Reddish dolostones in the upper Carrancas Formation have δ 13 C values ranging from +7.1 to +9.6‰, which is a unique C isotopic composition for the lowermost Bambuí Group but similar to values found in the Tijucuçu sequence, a pre-glacial unit in the Araçuaí fold belt on the eastern margin of the São Francisco craton. The stratigraphic position below basal Ediacaran cap carbonates and the highly positive δ 13 C values together indicate a Cryogenian interglacial age for the Carrancas Formation, with the high δ 13 C values representing the so-called Keele peak, which precedes the pre-Marinoan Trezona negative δ 13 C excursion in other well characterized Cryogenian sequences. Hence, The Carrancas Formation pre-dates de Marinoan Jequitaí Formation and represents an interval of Cryogenian stratigraphy not previously known to occur on the southern margin of São Francicso craton. Documentation of Cryogenian interglacial strata on the São Francisco craton reinforces recent revisions to the age of Bambuí Group strata and has implications for the development of the Bambuí basin. [ABSTRACT FROM AUTHOR]

High-resolution stratigraphic analysis was carried out on tidal microbial carbonates from the middle part of the Lagoa do Jacaré Formation from the Ediacaran-Cambrian Bambuí Group in the Ubaí area. In a 41 meter-thick section, sixteen lithofacies and three facies associations were interpreted as deposits of supratidal, intertidal, and subtidal settings. The tidal cycles are asymmetric and shallow upward, the high-resolution stratigraphic approach allowed inferences as to short-term and long-term fluctuations of sea level during deposition. The metric tidal ranges here described suggest strong tidal currents, which is incompatible with the giant enclosed sea model as an analog for Bambuí deposition, given that tidal ranges in suc seas are null or less than a few decimeters. Therefore, we suggest that the Ubaí carbonates were deposited in a semi-enclosed epicontinental sea subject to strong tidal forces when the formerly resticted Bambuí Basin reopened probably during deposition of the upper half of the Lagoa do Jacaré Formation, as suggested by previous isotopic data and now reinforced by our sedimentologic and stratigraphic field data. [ABSTRACT FROM AUTHOR]

A section investigated in the region of Paraopeba, Minas Gerais, provided detailed sedimentologic, stratigraphic and chemostratigraphic data from the Ediacaran Lagoa do Jacaré Formation, Bambuí Group, Southeast Brazil. This information allowed interpretation of tempestite facies in transgressive-regressive cycles, reinforcing the previously proposed storm-influenced sedimentation model and clarifying how it is associated with unusually high C-isotope values related to the Middle Bambuí Excursion (MIBE). Facies analysis of nine lithofacies identified at the GMD quarry based on field and petrographic descriptions showed distal tempestite facies grading upwards to a shallower, oncoidal/ooidal carbonate marine environment, then to basinal shales. The entire succession comprises a low-order transgressive hemicycle, recording the transition from a storm-influenced carbonate ramp to a siliciclastic-dominated platform. Chemostratigraphic data yielded high δ13C values ranging between +11.11‰ and +13.94‰. Our data contribute to the revision of the previously proposed interpretation and as well as to the understanding of paleoenvironmental conditions and C isotope signatures across the MIBE, near the Ediacaran-Cambrian boundary in the Bambuí Basin. [ABSTRACT FROM AUTHOR]

The Serra da Saudade Formation, Ediacaran/Cambrian Bambuí Group, cropping out along the ridge of the same name in Central-Western Minas Gerais, Brazil, contains important deposits of glauconitic siltstones associated with phosphatic rhythmite as well as other siliciclastic, volcaniclastic and carbonate lithofacies. Lithofacies indicate deposition by proximal and distal storm waves on a continental marine shelf. The basal gray siltstone and part of the green siltstone represent a transgressive systems tract. The glauconitic siltstone indicates sea level rise, with the maximum flooding surface located approximately at the interval of highest K2O content. Biogenic carbonate and an upward increase in sandstone beds are interpreted as a highstand systems tract. Gradual lateral facies changes reflect the transition from foredeep (to the west) to forebulge (to the east) deposition in a foreland basin as the final stage of a shallowing-upward second-order sequence. Black organic-rich limestone has d13C values between -8.78 and 9.79‰, negative d18O values from -11.50 to -9.35‰, and 87Sr/86Sr around 0.7075. This isotopic signature, similar to that of other Bambuí carbonates, indicates a probably-restricted depositional environment with organic sedimentation, methanogenesis and high evaporation rates from the Ediacaran through the early Cambrian period. [ABSTRACT FROM AUTHOR]

In order to investigate the geochemical responses of Earth's oceans and atmosphere after a Snowball glaciation, we studied an Ediacaran cap carbonate profile pertaining to the base of the Bambuí Group (Sete Lagoas Formation) in the central portion of the São Francisco basin, east central Brazil, for trace elements (including REE + Y) and C, O, Sr, Nd, Pb and Cr isotopes. The section can be divided in three portions, from bottom to top: (i) a two-meter thick cap dolostone preserving a drop of δ 13 C values from −3.8 to −4.2‰, overlain by (ii) a ca. 123 meters-thick, reddish limestone rhythmite deposited in a tidal flat, with an important isotopic shift observed at 60 m, with δ 13 C values below averaging −5‰ and above shifting abruptly to around −0.5‰; and (iii) a topmost ca. 2 meters thick black calcarenite with positive δ 13 C (+0.9‰) and 87 Sr/ 86 Sr = 0.7076. A new, tightly constrained Pb-Pb whole rock isochron of 608 ± 19 Ma provides additional support for deposition during the early Ediacaran. We put forward a model for the deposition of the Sete Lagoas cap carbonate which starts with the glacial aftermath, when the thin cap dolostone and the basal reddish limestone were deposited due to glacier melting and subsequent sea level rise, with important mixing of glacial meltwaters with anoxic bottom waters. A decreasing trend of εNd (630Ma) values, from −6 at the base to ca. −8 at the 60 meters-mark, indicates continued input of continentally-derived detrital particles to the basin. During this phase, intermittent subaerial exposure was responsible for meteoric diagenetic alteration, which shifted 87 Sr/ 86 Sr to higher values (>0.710) and δ 18 O towards lower values. Towards the top of the sequence, the late postglacial succession is marked by marine-like REE + Y (Y/Ho = ca. 46) and lower Al and Mn contents, reflecting the diminishing of glacial meltwater input, a renewed sea level rise, and a change to more distal depositional environments, away from the coastal lines. At this moment, a vigorous input of U(VI) and 53 Cr-rich Cr(VI), reflecting in a sharp rise of U/Th ratios and positive δ 53 Cr, suggests that fully oxygenated conditions finally predominated in post-glacial surface waters in the middle to late Ediacaran. Our results add to a growing body of data for other Ediacaran cap carbonate sequences around the world (e.g. Otavi Group, Namibia and Doushantuo Formation, China) that suggest that after ca 1 Ga of anoxia (the “Boring Billion”) following the first Great Oxygenation Event, the oceans became increasingly oxygenated after the end of the Marinoan glaciation ca. 635 Ma ago, ultimately leading to the explosion of complex macroscopic life that followed this Neoproterozoic Oxygenation Event. [ABSTRACT FROM AUTHOR]

A central tenet of the Neoproterozoic snowball Earth hypothesis is that glaciations ended synchronously. Although this condition is borne out by U-Pb and Re-Os geochronology, the time scale of deglaciation is much less than the intrinsic error of the highest resolution dating techniques, and consequently calibrating the pace and synchronicity of biogeochemical recovery from Cryogenian glaciations remains a challenge. Given the importance of obtaining a globally synoptic view of paleoenvironmental conditions and biological evolution during these extraordinary transitions, robust correlations and chronologies are imperative. Here we extend the negative triple oxygen isotope (Δ17O) anomaly previously documented in ca. 635 Ma postglacial cap carbonates to two new paleocontinents, Brazil and Norway. The global footprint of this geochemical signal coupled to its short duration provides a unique time datum that can be used to cross-correlate Marinoan postglacial cap carbonate sequences and track the geochemical evolution of the oceans during deglaciation. [ABSTRACT FROM AUTHOR]

Sedimentary rocks of the Sete Lagoas Formation, exposed in the left margin of the São Francisco river (Minas Gerais State, Brazil), were deposited on the Januária-Itacarambi basement high. They show both lateral and vertical rock stacking along continuous outcrops, allowing us to carry out detailed facies analysis and sequence stratigraphy studies. Our studies also integrate data from geological mapping, macro and microscopic petrography and high-resolution C and O isotope analysis. Eight facies and four facies associations make up a sequence composed by a transgressive tract in the base, and a high stand tract in the upper portion, separated by a maximum flooding surface. The high stand tract shows a progradation stacking from the basement high apex towards progressively deeper basement areas. This stratigraphic framework, associated with others stratigraphic and isotopic features, indicates that the now exposed Januária basement high also represents a paleo-high during the sedimentation event. Aragonite pseudomorphs and dolomites coupled with δ13C values of -5‰ characterize the basal carbonate of the transgressive tract as a cap carbonate. Records of the Cloudina fossil, recognized in the high stand tract, indicate a Late Ediacaran age for the upper portion of the studied stratigraphic sequence. [ABSTRACT FROM AUTHOR]

The Bambuí Group is a lithostratigraphic unit that comprises a mixed carbonate-siliciclastic platform deposited in a foreland basin. It is a 1st order sequence that filled the São Francisco Basin during the Ediacaran-Cambrian in southeast Brazil. The Lagoa do Jacaré Formation is the second carbonate unit of the Bambuí Group and is related to a 2nd-order regressive hemicycle composed of dark gray shallow water carbonates with high positive ẟ1³C values (>+10‰) related to the upper part of the Middle Bambuí Excursion (MIBE). We described four outcrops in the center-north of Minas Gerais state (Paraopeba, Curvelo, Montes Claros and Ubaí areas) coupled with ẟ13C and ẟ18O, and SEM-EDS analysis in order to support detailed facies analyses. One seismic line and three well logs in the south part of the Januária High were also used to define the stratigraphic framework of the Lagoa do Jacaré Formation in the Bambuí Foreland Basin system. Eight facies were interpreted from the outcrop data and grouped into five facies associations, that represent peritidal zone (FA1), ooidal sand shoals (FA5), tempestites of mid ramp (FA3), fine-grained carbonate of outer ramp (FA4), and fine-grained siliciclastic from offshore (FA2). The strong presence of terrigenous material (quartz, feldspars, muscovite, biotite, apatite) with some authigenic/diagenetic minerals (pyrite, titanite, rutile) in all facies are the main petrographic aspect of the studied carbonate rocks, related to high sedimentary input and some events during early diagenesis. FA1 with lower mean values of ẟ1³C (+9‰) predominates in the north, meanwhile FA3 is the main association in the south with higher ẟ1³C mean values (+12‰). This difference is probably related to the stratigraphic differences between the basal section (at south) and upper section (at north) of the Lagoa do Jacaré Formation. The Januária High was the main controlling element for the deposition of the carbonate ramp in the north sector of the basin, close to the Ubaí and Montes Claros cities. Probably, this structural high also played an important role as source area in the forebulge sector, uplifted by flexure due to the orogeny of the Brasília and Araçuaí (still in development) Belts (∼540-520 Ma). To the east, a N–S carbonate ramp system was developed in the back-bulge sector according to the main paleocurrents measurements. This ramp is related to a 300 m thickness section of the Lagoa do Jacaré Formation that was firstly identified and correlated to the successions on the surface using well logs, possibly registering at the top the decreasing in the ẟ1³C values, after the main stages of the MIBE probably in close association with Ediacaran-Cambrian boundary, related to the assembling of the Gondwana Supercontinent recorded in this region of southeast Brazil. • The Lagoa do Jacaré Formation (LJF) has more than 300 m of thickness. • The LJF deposited in a homoclinal carbonate ramp in the central Bambuí Basin. • The LJF increase in thickness from Januária High to Montes Claros. • a remarkable assemblage of siliciclastic minerals was first identified in the LJF. • The LJF was deposited in the back-bulge and forebulge of a foreland basin system. [ABSTRACT FROM AUTHOR]

The Chapada Diamantina region in the São Francisco craton of eastern Brazil is composed of sedimentary successions containing both Mesoproterozoic and Neoproterozoic carbonate levels, making it a key natural laboratory for understanding the fluctuations of Earth's biogeochemical cycles during its middle age. The ca. 1.4--1.2 Ga Caboclo Formation stromatolites yielded unfractionated δ53Crauth (authigenic) (-0.54‰ to +0.08‰). Ediacaran cap carbonates and phosphatic stromatolites of the Salitre Formation, on the other hand, yielded fractionated δ53Crauth reaching as high as +0.51‰, suggesting the input of 53Cr-rich Cr(VI), first delivered through meltwater-induced post-snowball Earth fluctuating redox conditions and then through weathering and mobilization under a fully oxygenated environment. The acquired data set highlights the very distinct redox conditions throughout the Proterozoic and reinforces the suggestion that after the Cryogenian global glaciations, Earth's atmosphere and hydrosphere became progressively oxygenated during the Ediacaran-Cambrian transition. [ABSTRACT FROM AUTHOR]

We combine U–Pb in-situ carbonate dating, elemental and isotope constraints to calibrate the synergy of integrated mountain-basin evolution in western Gondwana. We show that deposition of the Bambuí Group coincides with closure of the Goiás-Pharusian (630–600 Ma) and Adamastor (585–530 Ma) oceans. Metazoans thrived for a brief moment of balanced redox and nutrient conditions. This was followed, however, by closure of the Clymene ocean (540–500 Ma), eventually landlocking the basin. This hindered seawater renewal and led to uncontrolled nutrient input, shallowing of the redoxcline and anoxic incursions, fueling positive productivity feedbacks and preventing the development of typical Ediacaran–Cambrian ecosystems. Thus, mountains provide the conditions, such as oxygen and nutrients, but may also preclude life development if basins become too restricted, characterizing a Goldilocks or optimal level effect. During the late Neoproterozoic-Cambrian fan-like transition from Rodinia to Gondwana, the newborn marginal basins of Laurentia, Baltica and Siberia remained open to the global sea, while intracontinental basins of Gondwana became progressively landlocked. The extent to which basin restriction might have affected the global carbon cycle and climate, e.g. through the input of gases such as methane that could eventually have collaborated to an early Cambrian greenhouse world, needs to be further considered. [ABSTRACT FROM AUTHOR]

The basal units of the Vazante Group, the Santo Antônio do Bonito and Rocinha formations, present different stratigraphic records and younger ages than the rest of the group. These units are characterized by diamictites, sandstones, pelites and rare carbonates originated from subaqueous gravitational sedimentation. U–Pb geochronological data in detrital zircon indicate a Tonian maximum depositional age for both formations. The youngest zircon grains yielded ages ranging from 903 to 935 Ma. The main source for zircon is Paleoproterozoic (mainly Rhyacian and Orosirian) to Mesoproterozoic (Calymmian and Ectasian) areas being probably the São Francisco paleocontinent the main area. Due to the complete absence of ice-rafted debris within fine-grained sediments in the Santo Antônio do Bonito Formation, we interpret a gravitational reworking as the main process of diamictites deposition, probably during a period of ice retreat and sea level rise. The U–Pb data corroborate a lateral correlation between the Santo Antônio do Bonito and Rocinha formations with the glaciogenic Jequitaí Formation (Bambuí Group). From east to west, glacial sediments of the Jequitaí Formation were reworked probably by a slope-apron system during a late-glacial to post-glacial stage on the western margin of the São Francisco paleocontinent. Therefore, the Vazante Group can be divided into two successions: the upper Lagamar-Serra do Garrote formations and the lower Santo Antônio do Bonito-Rocinha formations. The Lagamar-Serra do Garrote sedimentation comprises a late Mesoproterozoic mixed carbonate-siliciclastic deposition in passive margins. The second succession is a gravitational slope-apron resedimentation and probably correlates with the Neoproterozoic glacial rocks of the Jequitaí Formation from the Bambuí Group. Finally, the collisional phase of the Brasília Belt was responsible for stratigraphic inversion, placing the older Lagamar-Serra do Garrote formations over the younger Santo Antônio do Bonito-Rocinha formations. • New regional and local geological mapping of the basal formations of the Vazante Group. • Gravitational sedimentation record in the basal formations of the group, relate to a subaqueous slope-apron system. • New U–Pb data of the Santo Antônio do Bonito and the Rocinha formations and its provenance change during Neoproterozoic. • Lateral correlations between Santo Antônio do Bonito and Jequitaí formations, during final stages of the ice retreatment. [ABSTRACT FROM AUTHOR]

• Middle Bambuí positive δ13C excursion (MIBE) in a restricted basin. • Higher δ13C carb , δ13C org , and δ34S signals during the MIBE. • δ13C carb and 87Sr/86Sr anomalies in the restricted Bambuí Basin. • Methanogenesis in sulfate-depleted oceans during the MIBE. • A heterogeneous biogeochemical landscape during the Ediacaran-Cambrian transition. The Ediacaran-Cambrian Bambuí Group in Brazil records an anomalously positive excursion in carbonate carbon isotopes (δ13C carb) with a sustained plateau of ca. +15‰ (aka the Middle Bambuí Excursion–MIBE). Considering that the δ13C carb signals in Ediacaran-Cambrian seawaters do not typically exceed +6‰, the MIBE therefore represents a profound carbon cycle anomaly in Earth's history. Although intensive studies have been done on the Bambuí Group, origins of the MIBE remain enigmatic. In order to better constrain the biogeochemical carbon and sulfur cycles during the MIBE, high-resolution chemostratigraphic analysis was conducted for both the plateau (i.e., Lagoa do Jacaré Formation) and the recovery part (i.e., lower Serra da Saudade Formation) of the MIBE. Chemostratigraphic profiles reveal remarkably different values in δ13C carb , δ13C org , δ18O carb , and δ34S pyrite between these two studied MIBE intervals. The new data show that the plateau of the MIBE is characterized by coupled higher δ13C carb , higher δ13C org, and higher δ34S pyrite signals compared with the recovery part of the MIBE. Based on multiple lines of sedimentological, geochemical, and model evidence, we propose that the possibilities of enhanced organic carbon burial and porewater methanogenesis are insufficient to explain the MIBE. Instead, local or regional controlling factors, including water-column methanogenesis, low-sulfate conditions, and enhanced carbonate recycling in a restricted basin may have played a role, independently or in unison, in generating this profound positive δ13C carb excursion. Therefore, the MIBE may reflect a regional event, instead of a global carbon cycle anomaly. We caution against the use of the MIBE in chemostratigraphic correlations on a global scale or any other attempt to infer global carbon cycling at that time. The biogeochemical landscape of the late Ediacaran-Cambrian basins and ocean margins may be more heterogeneous than previously thought. [ABSTRACT FROM AUTHOR]

One of the most essential and valuable applications of high-resolution sequence stratigraphy is reservoir zonation and characterization. Establishing a hierarchical chronostratigraphic framework comprising sequences at multiple scales is crucial to identify main reservoir heterogeneities that compartmentalize the fluid flow in the subsurface. In this context, this paper proposes a workflow that integrates different signal analysis techniques to identify sequences of multiple hierarchies from a series of stratigraphic data. The Continuous Wavelet Transform (CWT), Detrend Error Log (DTEL), and Integrated Detrend Error Log (INDTEL) techniques are utilized to process gamma-ray data obtained from outcrops of the Yacoraite Formation, which are conventionally employed as analogs for reservoir characterization. Our results suggest that CWT fits better with higher frequency cycles, while INDTEL shows a good fit with medium frequency cycles. In addition to these techniques, Hidden Markov Models were also applied, predicting T-R cycles as hidden states from the facies transition matrix and possible occurrence of missed beats. All these methods were scripted in the Python programming language, enabling the generation of fast and interactive outputs. This approach brings parameters that can guide the construction of stratigraphic models by automated processes. • Multifrequency transgressive-regressive cycles were obtained from spectral decompositional techniques on Gamma-Ray proxies. • High-Frequency output curve from Continuous Wavelet Transform has direct relationship with high-frequency transgressive-regressive cycles. • INDTEL method is a powerful tool to detect hidden trends and well correlation. • Hidden-Markov Models show high-frequency transgressive-regressive cycles as hidden states from facies transition • The integrated aplication of the methods proves to be a promising tool to help detect missed-beats. [ABSTRACT FROM AUTHOR]

• Extensive new Ba isotopic survey of modern barites. • First Proterozoic Ba isotopic results. • Provides genetic model for enigmatic post-Marinoan barite formation. • Provides evidence for stratified post-Marinoan ocean. • Provides arguments for why barite horizons are confined to Marinoan and not Sturtian or Paleoproterozoic strata. Measurements of triple oxygen isotope ratios in barite horizons within post-Marinoan cap carbonates have provided some of the most compelling evidence that the Marinoan glaciation was a Snowball Earth event. However, the origin of these barite horizons remains unresolved. To constrain the Ba sources, and thus formation mechanisms of these horizons, we analyzed the Ba isotope composition of post-Marinoan barite deposits from Northwest Canada, Northern Norway, Brazil and South China. We augment these analyses with a Ba isotope survey of almost 100 modern and ancient additional barite measurements, including samples from pelagic (or 'marine'), hydrothermal, terrestrial, Proterozoic stratiform and cold seep environments. Unlike modern cold seep or terrestrial barites, we find that globally-distributed post-Marinoan barites exhibit a relatively narrow isotopic range, suggesting a well-mixed, effectively limitless Ba source. Moreover, post-Marinoan deposits exhibit a similar mean Ba isotope composition to modern marine barites, which we interpret as evidence of a marine Ba source. Considered alongside existing geochemical, geological, and new Ba isotope survey data, we conclude that Ba in barite horizons was sourced from a well-mixed, Ba-replete but SO 4 -poor reservoir that accumulated during the Marinoan Snowball Earth interval. This deep Ba reservoir was then transported upward—either by ocean circulation or dolomitization of underlying cap carbonates—and was brought into contact with continental weathering-derived sulfate in a post-glacial meltwater surface layer. Thus, in addition to providing a plausible mechanism for generating globally-synchronous deposition of post-Marinoan barite horizons that reconciles all existing geochemical and geological data, our results demonstrate the utility of Ba isotopes to interrogate the origin of enigmatic barite deposits throughout the sedimentary record. [ABSTRACT FROM AUTHOR]

We apply trace element analysis of syn -sedimentary pyrite to track the redox and nutrient variations in the Ediacaran-Cambrian Bambuí Group of eastern Brazil. Sedimentary pyrite from black shales interleaved within the basal cap carbonate of the 635–600 Ma Pedro Leopoldo Member, deposited in an open marine setting connected to the global sea, preserve high Mo up to >200 ppm, erratic enrichment of micronutrients such as Cu, Ni, Ba, Zn and uniform enrichment of Se. This indicates the importance of oxidative continental weathering and development of an enhanced Redox Sensitive Elements (RSE) dissolved reservoir on the aftermath of the Marinoan glaciation, with atmospheric O 2 levels, calculated from Se/Co ratios of pyrites, around 2.5–3.5 wt%. A shallow oxic layer over deep euxinic realms made possible by high concentrations of dissolved sulfate was probably maintained up to the late Ediacaran, during deposition of the Cloudina-bearing Lagoa Santa Member (585–540 Ma). Upsection, however, radical shifts to muted Mo concentrations and overall low micronutrient concentrations are recorded in the Serra de Santa Helena Formation, with O 2 levels plunging below 1 wt%. This indicates the development of ferruginous bottom water conditions in a sulfate-poor setting, due to restriction of the basin by the encircling Brasiliano mountains that formed Gondwana. The restricted, oxygen-poor and nutrient-depleted conditions caused the demise of complex life forms and hampered the development of typical Ediacaran-Cambrian ecosystems. Basin re-connection might have occurred during deposition of the Lagoa do Jacaré Formation, with independent proxies such as local tidal facies indicating a return to more ventilated conditions in the upper Bambuí Group. Our results highlight the importance of basin restriction and connection over coupled redox-nutrients variations during the development of Ediacaran-Cambrian ecosystems. • Sedimentary pyrite trace element concentrations of the Bambuí Group. • Basin restriction and connection controls coupled redox-nutrients variations. • Radical shifts in nutrient and oxygen levels in the Ediacaran-Cambrian transition. • Redox-nutrient variations control the development of complex life forms. [ABSTRACT FROM AUTHOR]

The Borborema Province of northeast Brazil occupies a strategic position in the central portion of West Gondwana, linking three of its major cratonic constituents: the São Francisco- Congo, Amazon, and West Africa cratons. The southern portion of the province, the Riacho do Pontal fold belt, comprises an association of exhalative rocks with metabasalts having transitional mid-oceanic ridge basalt geochemistry (Monte Orebe Complex) that suggests the preservation of remnants of Neoproterozoic oceanic crust. This view is supported by geophysical data: the Riacho do Pontal fold belt corresponds to the inflexion of a paired positive-negative Bouguer anomaly similar to other Precambrian suture zones. Sm-Nd isotope data for the metabasalts yield a whole-rock isochron age of 819 ± 120 Ma with an initial εNd(t) = +4.4, indicating derivation from a depleted mantle source. The onset of subduction within the Borborema Province (ca. 630 Ma) caused the inversion of basins and obduction of slices of oceanic crust. In this scenario, the Riacho do Pontal fold belt represents a complete late Neoproterozoic plate tectonics cycle involving the collision of the São Francisco craton (lower plate) with the Pernambuco-Alagoas block (upper plate). This interpretation challenges current views that the Borborema Province has acted as a coherent block since Paleoproterozoic time (part of the Atlantica supercontinent), suggesting instead a dynamic setting, where multiple plates interacted during the Proterozoic. The Monte Orebe ophiolite provides a link with other Cryogenian oceanic crust occurrences in central Brazil and West Africa, indicating the preservation of a transcontinental Neoproterozoic suture zone in the heart of West Gondwana. [ABSTRACT FROM AUTHOR]

Abstract: Remnants of a Neoproterozoic glaciation in east central Brazil are represented by thin diamictite layers (Jequitaí Formation and correlative units), locally overlying striated pavements on the São Francisco craton. The diamictites are covered by the Sete Lagoas Formation of the basal Bambuí Group, which is generally accepted to be a typical cap carbonate sequence. Although most authors have preferred a mid-Cryogenian (post-Sturtian) age for it, based mainly on Pb-Pb whole rock data, the Sete Lagoas Formation bears lithostratigraphic and isotopic characteristics that are identical to early Ediacaran cap carbonates worldwide, including a basal thin (0–10m) pale and flinty cap dolostone, preserving a drop in δ13C values from around −3.2‰ to −4.5‰ with associated δ18O around −5‰, and crystal-fan facies interpreted as aragonite pseudomorphs. Ediacaran zircons have been recovered from the middle of the Sete Lagoas Formation, constraining the deposition of its upper half to be younger than 610Ma (). Although there is an unconformity below the point where the zircons were collected, it is short-lived, as suggested by the identical, typically Ediacaran 87Sr/86Sr values above and below (0.7074–0.7076). Carbonate clasts from the Jequitaí Formation and correlative diamictite-bearing units in the fold belts that surround the São Francisco craton (Canabravinha and Serra do Catuni formations) display similar ranges in δ13C (−6.7 to +2.6‰), suggesting the erosion of a pre-glacial carbonate platform with negative δ13C values (i.e. the Islay and/or Trezona anomalies). The cratonic Carrancas Formation, on the other hand, yielded pale dolostone clasts with δ13C in a small range between −4.2 and −3.4‰, and δ18O values around −6.5‰. These clasts could be derived from the cap dolostone unit itself, in which case the Carrancas Formation would represent resedimented basal Sete Lagoas Formation and imply that sections of the Sete Lagoas Formation sitting atop the Carrancas Formation are incomplete. The base-truncated sections have confused previous attempts to correlate the Sete Lagoas Formation with other cap carbonate successions. In light of the available lithostratigraphic, isotopic and U-Pb zircon data, we propose that the Sete Lagoas Formation represents a basal Ediacaran cap carbonate sequence (∼635–610Ma) deposited after the Marinoan glaciation in east central Brazil. [Copyright &y& Elsevier]

Metallogenetic model for the Buritirama Mn-carbonate rocks. [Display omitted] • The dolomitic marbles associated with the Buritirama Formation record a likely marine geochemical signature. • δ13C values of dolomitic marbles are thought to be an expression of the Lomagundi Carbon Isotopic Excursion. • Geochemistry and isotopes data of Mn-Carbonate rocks indicate a multi-stage metallogenetic model involving the manganese marine cycle. The Mn-bearing Buritirama Formation is composed of clastic and chemical metasedimentary rocks representing a Rhyacian platformal basin (ca. 2.18–2.06 Ga) that limits the northern border of the Archean-Paleoproterozoic Carajás domain with the Paleoproterozoic Bacajá domain in the southern Amazon Craton, northern Brazil. The Buritirama Formation is divided into three main stratigraphic units. The Lower and Upper units consist of a basal quartzite followed by carbonate–silicate rocks (marls), dolomitic marbles (dolostone) and minor biotite schist while the Intermediate Unit consists of Mn-carbonate rocks topped by a supergene Mn-oxide deposit (Cenozoic age). These rocks were deformed and metamorphosed during the Transamazonian event (ca. 2.06 Ga). Geochemical data from dolomitic marbles (Lower Unit) exhibit negative Ce anomalies, high Y/Ho ratios (ca. 48) and seawater-like REE + Y patterns that reinforce an open platform setting for the Buritirama basin. Positive δ13C values (+3.2‰ to +5.0‰ V-PDB) for dolomitic marbles are considered to be an expression of the Lomagundi Carbon Isotopic Excursion. The metallogenesis of Mn-carbonate rocks is evaluated based on redox-sensitive trace elements (e.g. Zn and Ni), PAAS-normalized REE + Y patterns and δ13C values (−2.56‰ to +0.15‰ V-PDB) and point out to a classical multi-stage redox-controlled Mn-model involving: i) a primary hydrothermal fluid source related to ocean vents and/or normal faults; ii) microbially-mediated reduction of Mn-oxides particles at the ocean bottom; and iii) reactions between Mn2+ and CO 3 2− (organic matter and seawater related), giving rise to diagenetic Mn-carbonates. The Rhyacian age, Mn deposits, and presence of Lomagundi-like δ13C allows to correlate the Buritirama Formation with the Águas Claras Formation within the Carajás domain further south, thus establishing an important metalliferous event that was up to now largely overlooked within the southern Amazon Craton. [ABSTRACT FROM AUTHOR]

The Serra da Saudade Formation is part of the Bambuí Group, a cratonic cover from the western São Francisco craton. It is composed by siliciclastic sediments deposited in a foreland basin during a transgressive event. The Serra da Saudade Formation is mainly represented by rhythmites, siltstones (locally glauconitic) and rare sandstones. The glauconitic siltstone was deposited during a maximum flooding surface and sediment starvation, which allowed high concentrations of probable volcanic-sourced potassium. The interpretation of the depositional age of the Bambui Group had multiple turnovers in the last decades. Finding and dating synsedimentary volcanic rocks is essential to solve this conundrum. This paper presents the first U-Pb direct dating of the Bambuí Group from zircon grains recovered from a volcaniclastic layer interbedded with glauconitic siltstones from the upper Serra da Saudade Formation. A total of 107 U-Pb ages were obtained by LA-ICP-MS and plotted into a Concordia diagram. The provenance signature comprises a wide range of detrital zircon ages (1.0–2.8 Ga). These data represent inherited zircon grains incorporated into the magma during magmatic activity that produced the volcanic sediment, or to dilution and reworking of volcanic ashes that mixed to fine-grained clastic sediments prior to deposition. A significant amount of 10 highly concordant, prismatic zircon grains clustered into a well constrained age of 520.2 ± 5.3 Ma, which represent the explosive volcanic eruption age, and by extent, the depositional age of the upper Serra da Saudade Formation. Since the currently final thrust stacking ages from the Brasilia Belt and the Araçuaí Belt are dated ca. 600 and 540 Ma, respectively, one must carefully look for the real age of the deformation event that affected the Bambuí Group over the São Francisco craton. Image 1 • Stratigraphy, petrography and geochronology of Serra da Saudade Formation, Bambuí Group. • The glauconitic siltstone was deposited in a foreland basin during low sedimentation rates and related to volcanic processes. • The volcanoclastic layer described in the upper Bambuí Group reveals a sedimentation age of 520.2 ± 5.3 Ma. • The Bambuí Group spanned the Ediacaran-Cambrian boundary and was deformed during the Cambrian Period. [ABSTRACT FROM AUTHOR]